It depends upon:
1. How accurate is the birth, horary question, or event time?
2. Placidus is really time-sensitive, but if the birth time is only an estimate, then there's no point in placing much faith on its house cusps.
3. High latitude births generate their own problems of house division. Imagine that you're near the Arctic Circle, with very long winter nights and very short summer nights, for example. Scandinavian astrologers apparently prefer equal houses, but then these are pretty artificial.
4. Many horary astrologers believe that Regiomontanus produces the best results.
5 Many traditionalists and Vedic astrologers prefer whole signs, and use methods other than house cusps to determine timing.
6. Koch and some of the newer house systems were designed to upgrade Placidus. You may or may not detect much difference.
7. Fundamentally the "best" house system is the one that best describes the given individual, question, or event. To determine this, it's important to have a good grasp of the many meanings of each house. If someone is a real home-body, for example, it would make more sense to see a focus on the 4th house, rather than the 9th house. But then the 9th house home-body might be an "armchair traveler" with a lot of good books about distant places. Or philosophy books. So you really have to play around with the different systems.
Astrodienst has a huge selection of house system options.